Method for protecting painted work-pieces in a bake oven

ABSTRACT

A polysiloxane oven coating for use in paint baking ovens to trap undesirable solid particulate matter and thereby prevent its deposition on the baking paint film. The coating can be employed effectively without causing paint defects in the finished paint film.

United States Patent 1191 Cavanaugh, Jr.

[ Jan. 8, 1974 METHOD FOR PROTECTING PAINTED WORK-PIECES IN A BAKE OVEN[75] Inventor: Robert E. Cavanaugh, Jr., Detroit,

Mich.

[73] Assignee: Amchem Products, Inc., Ambler, Pa.

[22] Filed: Jan. 12, 1972 [21] Appl. No.: 217,219

52 US. Cl ..1l7/97,117/95,117/119.8, ll7/1l9.6, 117/122 PS, 117/132 BS,

51 1111.01 B44d l/46, F26b 3/00 581 Field of Search 117/132 BS, 161 ZA,

117/] 19.6, 97,122 1 5,122 R, 95,1198; 34/81, 80, DIG. l

[56] References Cited UNITED STATES PATENTS 3,669,503 6/1972 Zimmermann117/95 X FOREIGN PATENTS OR APPLICATIONS 1,042,215 9/1966 Great Britain117/ll9.8

Primary Examiner-Ralph Husack Attorney-Ernest G. Szoke et al.

1571 ABSTRACT,

A polysiloxane oven coating for use in paint baking ovens to trapundesirable solid particulate matter and thereby prevent its depositionon the baking paint film. The coating can be employed effectivelywithout causing paint defects in the finished paint film.

4 Claims, No Drawings METHOD FOR PROTECTING PAINTED WORK-PIECES IN ABAKE OVEN BACKGROUND OF THE INVENTION The solid particulate matterordinarily found suspended in paint bake ovens such as dust,lint, andrust particles, are carried into the oven by air currents, and depositon the curing paint film. The deposit of these particles on the paintedworkpieces passing through the oven contributes to later paint defectsand failure.

Attempts have been made to prevent the unwanted particulate matter fromentering paint bake ovens. In. most cases, these attempts have beenmechanicalin nature and have included, for example, filtering theincoming air entering the paint bake oven, maintaining a.

positive pressure in the oven to prevent the drawing in of unfilteredair, and covering both entrance and exit tunnels of the oven. Thesemechanical attempts have been successful to a small degree in reducingthe amount of particulate matter in the ovens, but have not eliminatedthe problem created by the undesirable materials which enter the ovensdespite the mechanical precautions;

Once the undesirable particles have entered the baking oven, theapproach commonly employed is to attempt to trap the solid. matter,thereby preventing its deposition on the fresh paintfilm. Numerousmaterials have been employed to coat oven walls and floors in an attemptto trap the particulate matter and keep it out of the circulating airstream in the oven, thereby preventing its deposition on the workpiecespassing through the oven. Examples of the materials employed by the artare polyisobutylene, castor oil, and oxygenated petroleum hydrocarbons.Most materials proved unsuccessful or succeeded in only providinglimited protection forshort periods of time. Due to the temperature ofthe ovens during the dryingand curing process, especially the bakingtemperatures employed in the processing of most acrylic finishes, thematerials are either thermally degraded or volatilized and becomecompletely ineffective. The high temperatures, usually exceeding 350F,succeed in degrading the materials.

It is an object of this invention to provide an oven coating which willtrap the solid particulate matter in paint bake ovens and prevent itsdeposition on the drying paint film. I

It is also an object of this invention to provide a method forprotecting the painted workpiecestreated; in paint bake ovens andprevent the deposition ofundesirable particulate matter on the paintedworkpieces.

An additional object of this invention is to provide a coatingcomposition to be administered to the walls and floors of paint bakeovens, said composition able to withstand bake temperatures exceeding350F without degradation and loss of effectiveness.

A concomitant object of'the present invention is to provide an ovencoating that can be incorporated in a ready to use formulationconsisting of an anti-oxidant as well as solvents and thickener, inaddition to the polysiloxane in order to make a compatible and usefulmixture.

Additional objects of this invention will be apparent from thedisclosure which follows.

DETAILED DESCRIPTION This invention provides for a method for protectingpaintedworkpieces by preventing the deposit of unde- 2 sirablerparticulate matter on. the workpieces during treatment'in apaint bakeoven, comprising'applying to the oven surfaces an ovencoatingconsisting'of a polysiloxane represented by theformula:

wherein n is between 1,100 and 2,200. It will be appreciated that thepol'ysiloxanes represented by the above formula and suitableforuseinmethods of the present invention are generally known compounds,which are readily obtainable commercially or by conventional synthesiswmethods well known to those skilled in the art.

The polysiloxane can be formulated with other constituents to form anoven coatingcomposition containing polysiloxane, ananti-oxidant, athickener, and such solvents as are necessary to-producea compatiblemixture givingthe desired results when employed in accordance with themethod provided herein.

It willbe appreciated that theoven coating composition of the presentinventionwill have a viscous consistency. In the preferred; embodimentof the present invention, the polysiloxane to be employed intheformulation should have a. viscosity of from about 30,000cent-istokes to about 100,000 centistokes when measured' at atemperature of 25C in accordance with A.S.TIM. Standard MethodrD-445.Theepolysiloxane mustpossess this highviscosity sothatit can be appliedon. both horizontaland vertical surfaces and due to its heavyconsistency willv hold on such surfaces.

Inorder to formulate the oven coating composition, significant amountsof solvent and anti-oxidant will or dinarily be used. The polysiloxane.should be present in an amount from about 10 percent to about 50 percentby weight.

The anti-oxidant is employed to inhibit thermal degradation ofthepolysiloxane. It has been found that incorporation of the antioxidantin the formulation can increase the useful life of the appliedoven coating, compared to that of an uninhibited coating, at thetemperatures normally encountered during use.

Typical examples of antioxidants suitable for use in the presentinvention are phenothiazine, phenylalphanaphthyl amine,vN-stearoyl-p-aminophenol, N-lauroyl p aminophenol, trimethyldihydroquinoline polymer, and diphenyl ethylene diamine. The antioxidantcan be present in the oven coating composition in" an amount from about0.5 percent to about 2.0 percent by weight of the polysiloxane.

In preparing. formulations in accordance with the present invention ithasbeen found useful to rely upon certain solvents in order'to provide amore easily handled and applied product, as well as to enhance thestability of the polysiloxane and anti-oxidant. Typical examples of thesolvents which can be employed in the present invention are aliphatichydrocarbons, aromatic hydrocarbons, and halogenated hydrocarbons. Thesolventscan be present in an amount from about 50 percent to about.percent by weight.

In order to hold the coating on vertical surfaces until the solventsevaporate, a thickener may be employed.

A typical example of a suitable thickener isN-alkylgamma-hydroxy-butyramide. When a thickener is used, it willnormally be present in an-amount from about 0.05 percent to about 1.0percent by weight. When N- alkyl-gamma-hydroxy-butyramide is used as athickener, an ancillary benefit derived from its use is a reduction inthe rate of corrosion of ferrous metal surfaces to which the coating isapplied.

A surprising aspect of the present invention is that the compositionemployed herein, when applied to the appropriate portions of the bakingovens, does not contribute to any failure of the paint films beingtreated in the oven. No contamination of the paint film is evident andno paint defects can be observed. This is an important advantage of thepresent invention, since siliconecontaining coatings ordinarily willcontribute to such defects in the paint film due to the migration of thesilicone to the painted workpiece. In fact, the art has specificallyavoided the use of silicone-containing compositions.

The compositions of the present invention are used in accordance withwell known practices in the art. An effective amount of the compositionis applied to the walls and/or fioor of the oven by any convenientmethod such as brush, roller coating, or spraying. The resultingcoating, after evaporation of any solvents, provides a non-oxidizingfilm having a thickness from about 0.5 to 3 mils, which will remain softand tacky, and will trap and hold airborne dirt particles, whichotherwise might settle on the curing paint film. It has been found thatthe coating will maintain its stability and is able to withstandtemperatures as high as 500F for periods up to 6 months. In addition,the tendency of ferrous surfaces to rust due to the corrosive nature ofthe vapors from the drying paint will be significantly reduced.

Reference is now made to the following examples which set forth ovencoating compositions and the method of the present invention, it beingunderstood that such examples are presented for the purpose ofillustration only and are not necessarily limiting upon the scope of theinvention.

EXAMPLE I An oven coating 'composition was prepared and contained thefollowing:

% by Weight Dimethyl polysiloxane l3.0 Anti-oxidant 0.2

Naphtha EXAMPLE 2 The following oven coating composition was' employedin this procedure:

% by Weight Dimethyl polysiloxane 3 Anti-oxidant 0.2 Naptha 86.65

Thickener (N-alkyl-gamma-hydroxy-butyramide) .15

The composition was prepared by dissolving the dimethyl polysiloxane inabout an equal weight of the VM+P naphtha, then blending in theanti-oxidant and mixing until completely uniform. This mixture was thenadded to the balance of the VM+P naphtha, and the resulting compositionheated to F. The previously melted thickener was then added, and thesolution mixed until completely uniform. The composition had a specificgravity of 0.774 at 60F.

The foregoing composition, when applied to the walls and floors ofapaint bake oven resulted in a 20 percent reduction in paint defects whencompared to controls baked in the oven without the oven coatingcomposition present.

l claim:

1. A method for protecting painted workpieces from the deposition ofundesirable particulate matter in a paint bake oven comprising applyingto the oven surfaces a composition which remains soft and tacky duringbaking of the workpieces, said composition consisting essentially of apolysiloxane having the formula:

i l E cH,- sio si-o sicH CH, CH, CH,

additionally contains an effective amount of thickener.

2. The method of claim 1 wherein the composition additionally containsan effective amount of anti-oxidanT.
 3. The method of claim 1 whereinthe composition additionally contains an effective amount of solventwhich evaporates after application of the composition to the ovensurfaces and during baking of the workpieces.
 4. The method of claim 1wherein the composition additionally contains an effective amount ofthickener.